Table 4 illustrates the effect of increasing 
from zero
to infinity. For all functions and for both long and short
queries performance improves fairly smoothly with 
. For BM11 the
increase in average precision is 37% on the long queries and 12% on
the short. It is to be expected that 
would have a greater
effect with the long queries, in which there are many ``noisy'' terms
and in which most of the more apposite terms are likely to occur more
than once. However, high values of 
increase the performance of BM15
by 24% even on the short queries.
: Effect of varying the query term frequency parameter 
